1. Field of the Invention
The present invention relates to glue applicators for collating machines, and more particularly, to glue applicators utilizing glue nozzles which contact the moving web. 2. Prior Art
Collating machines, such as that disclosed in U.S. Pat. No. 3,682,468 which issued to the assignee of the present invention, are used to fabricate paper forms comprising a plurality of sheets which are glued together, typically at their longitudinal edges. Such collating machines typically include horizontally spaced spindles on which are mounted paper supply rolls and feed cylinders around which the webs from the paper supply rolls are threaded to be collected in overlapping relation along a horizontal path, typically a pin conveyor. Those feed cylinders located adjacent the horizontal path include peripherally spaced, outwardly projecting, retractable pins which engage longitudinally spaced marginal perforations within the webs to assure registration and positive feeding of the assembled webs along the path. These cylinders are often called "pin cylinders". In other collating machines, pin cylinders are not used. Instead, pinless back-up rolls are used, but those collators still employ pin conveyors to transport the web.
Collating machines also include glue systems the basic elements of which consist of one or more glue nozzles, a source of glue under pressure, and a supply line connecting the nozzles with a source of glue and including a valve which can be opened and closed to start and stop the flow of glue through each nozzle. Each nozzle is directed toward a moving web at a location prior to its engaging a second moving web so that glue may be applied prior to the overlapping of the webs.
Prior art glue systems are, in general, of two basic types: those utilizing nozzles touching the moving web to which glue is applied, and those utilizing noncontacting nozzles, in which the glue nozzle is spaced slightly away from the moving web and the glue traverses a slight air gap before it contacts the moving web. With either system it is desirable to employ a glue nozzle with a small diameter orifice, typically the size of a hypodermic needle, to provide a thin, continuous glue line of uniform width. This line must be consistent in quality to allow high speed collating without glue build-up and tenting of folded forms. The two systems have different advantages and disadvantages.
Advantages of glue systems utilizing noncontacting nozzles are: (a) the glue nozzle does not create drag upon the web, (b) the lack of contact between the nozzle and the web eliminates nozzle wear problems caused by the abrasion of the web against the tip of the nozzle, (increasing nozzle life) and (c) presence of an air gap between the tip of the nozzle and the surface of the moving web can accommodate variations in the distance between the surface of the web and the tip of the noncontacting nozzle. To maintain close spacing between the tip of the noncontacting nozzle and the moving web, noncontacting nozzles are usually positioned on the collating machine to deposit glue on a supported area of a web, as where the web passes over a pin cylinder or back-up roll.
Disadvantages of noncontacting nozzles result from the necessity of the glue having to traverse the air gap before contacting the moving web. Since the glue is not restrained by the nozzle orifice as it contacts the web, the resultant glue line may vary in width and in thickness, and if the flow rate of glue does not match the web speed at a given instant, portions of the deposited glue line may contain an excessive or an insufficient amount of glue. Adjustment of the air gap is critical, and the maintaining of a proper air gap may result in excessive down time. The maximum speed a collator may reach may be reduced, due to the inherent sensitivity of this type of nozzle.
Glue systems utilizing a contacting nozzle can more easily produce a glue line on a moving web that is consistent in width and thickness. The glue flows through the tip of the nozzle onto the paper in a thin film, constrained by the dimensions of the orifice of the nozzle. The viscosity of the glue causes the glue which has contacted the paper to draw glue from the nozzle at a rate that equals the speed of the web, thereby reducing inconsistencies in glue flow rate.
However, contacting nozzles cause drag on a moving web which can disrupt feeding of the web through the collating machine, and may cause weaving of the web and/or glue line. A wear factor is introduced since the moving web can abrade the nozzle tip, and it is necessary to make contacting nozzles of abrasion-resistant materials, such as metal, to prolong the useful life of a nozzle. But metal nozzles tend to have high spring rates and low flexibility, thus decreasing the capability of the glue nozzle to compensate for variations in the distance of the web surface from the body of the nozzle. In addition, contacting nozzle systems require high system pressures which tax the individual components, such as pumps, valves, and fittings, leading to low reliability and flow control problems.
To eliminate these disadvantages, contacting type glue nozzles are usually positioned such that glue is applied to a moving web as it passes between two cylinders and is relatively unsupported. The flexibility of this space of web serves to compensate for variations in tautness, which causes flutters of the web. Another means of compensating for the inflexibility of noncontacting nozzles is to fix a brush in contact with the moving web opposite the glue nozzle, to provide a flexible support for the web and accommodate web flutter. In addition, positioning of the nozzle and brush requires precise adjustment and the maximum speed at which a collator may function effectively is reduced if a brush and nozzle combination is used. Neither arrangement enhances the consistency or quality of the glue line, nor facilitates feeding paper through the collator.
In both contacting and noncontacting nozzle systems, high system pressure causes glue to seep through the nozzle after the machine has stopped and the line pressure has returned to atmospheric. If the web is no longer in motion, this causes a large deposit of glue to be made on the web which may render that portion of the web useless and foul the mechanical parts of the collator.
Accordingly, a need exists for a glue system which can apply a consistent line of glue to a moving web with a quality comparable to that of glue systems utilizing contacting nozzles, yet can easily compensate for variations in distance between the web and nozzle body, has a low drag factor on the web comparable to that of systems utilizing noncontacting nozzles, and which terminates flow at the nozzle tip when the flow of glue through the supply conduit is stopped. Such a system must be quick and easy to set up, result in high quality forms free of glue build-up and tenting, and be capable of high speed operation.